Cyclic halo-phosphate and thiophosphate esters, commonly known as phospholanes are well known in the literature, as, for example, British Pat. No. 766,766. These compounds have been prepared by reacting 1,2- or 1,3- glycols with a phosphoryl or thiophosphoryl trihalide in the presence of a tertiary base such as pyridine. Aromatic cyclic halo-phosphate and thiophosphate esters have also been known for a long time. See, for example, L. Anschuetz and W. Broeker, Ber., 61B (1928) 1264 (C.A., 22: 4113).
Benzylic cyclic halo-phosphate and thiophosphate esters, have, however, not been disclosed in the literature. This is surprising particularly since o-benzylic cyclic phosphate and thiophosphate triesters have been reported recently as being useful insecticides. See Belgian Pat. 633,481 (C.A., 61: 9541a) and the publications of M. Eto and co-workers [Agr. Biol. Chem., 29(1965)243; 30(1966) 181 (C.A., 64; 17627f)]. These latter compounds were invariably prepared by reacting an o-hydroxybenzyl alcohol with an alkoxy phosphoryl or thiophosphoryl dihalide in the presence of a base such as pyridine or other tertiary amine.
Our experiments have shown that the standard procedures used to prepare cyclic halo-phosphate and thiophosphate esters cannot be used to prepare the benzylic analogues. Reaction of an o-hydroxy-benzyl alcohol with a phosphoryl or thiophosphoryl trihalide in the presence of a tertiary base was found to yield polymeric tars. Cyclic phosphorus-containing esters having the general formula (II) ##STR2## wherein R is an alkyl radical, R' is a hydrogen atom or an alkyl radical, X is oxygen or sulfur, and Y is an oxygen or an N-aryl-radical, have been known to possess significant insecticidal activity (British Pat. No. 987,378).
These compounds have been prepared by reacting for example, O-hydroxy-benzyl alcohol or its derivatives with either alkoxyphosphoryl dichloride or alkoxy thiophosphoryl dichloride in a solvent in the presence of a dehydrochlorinating agent, for example, a tertiary base such as pyridine or triethylamine.
More recently, an improved process was disclosed (Japanese Pat. No. 7,028,183) whereby the reaction is conducted in an aqueous alkaline hydroxide medium to give a much higher yield.
All of the previous processes, however, are based on the use of alkoxy phosphoryl or thiophosphoryl dichloride as one of the reactants. These, however, are unstable liquids, having a very short shelf life. Furthermore, they are difficult to prepare particularly in a pure form and the cyclic phosphorous esters prepared from thiophosphoryl dichloride are vile smelling due to impurities in the reaction product which are not readily removed.